1. Field of the Invention
The present invention relates to an oscillation damper for a hand-held power tool and, in particular, for a hammer drill, a combination hammer and chisel hammer.
2. Description of the Prior Art
An oscillation damper represents an oscillation-capable sub-system that consists of an abstract oscillating mass, an abstract spring, and an abstract damper and that is not necessarily needs to be explicitly formed of concrete components. In particular, the abstract damper often is not formed by concrete components but nevertheless functions by using friction and flow losses which practically always present. There exist two types of dampers, conventional passive oscillation dampers that exclusively are self-excited, and actively controlled dampers.
By a suitable selection of spring constant and mass, in a passive damper, its natural frequency can be so dimensioned that it is closed to a to-be-damped interference frequency, in the present case, to the oscillations of the outer housing.
French Publication FR 2,237,734 discloses use of a passive oscillation damper for a preventing oscillations of a housing of a percussion hand-held power tool.
U.S. Pat. No. 4,478,293 discloses synchronization of operation of two passive oscillation dampers by using compressed air pulsation.
According to European Publication EP 1 415 768, an oscillation damper is located in a damper housing that is releasably form- or forcelockingly secured on remaining outer housing of the hand-held power tool, on a side surface of the housing remote from the handle and opposite thereto.
In International Publication WO 2006/022345, an oscillation damper is located in the outer housing on its side remote from and opposite the handle. A compact damping mass is compressively preloaded with two side, opposite, helical compression springs the spring force of which is combined, whereby the natural resonance frequency is increased.
Because a passive oscillation damper usually has a narrow strip-shape, the natural frequency should almost always correspond to the to-be-damped interference frequency. In percussion hand-held power tools, the impact frequency can, however, change, in particular, dependent on an operational mode selected by a tool user.
Accordingly, an object of the present invention is to provide an oscillation damper for a hand-held power tool with a switchably changeable impact frequency.